Exhaust systems for three cylinder, two-cycle engines which utilize positive pressure pulses from adjacent cylinders to pulse charge the cylinder and returning negative pressure pulses to improve scavenging have been disclosed in U.S. Pat. No. 3,692,006 and in Mellde et al, Some Experiences of Two-Cycle Engines as Power Unit for a Passenger Car, 65008 (954A), SAE Transactions, 1966.
Another type of exhaust system for a three cylinder engine is disclosed in U.S. Pat. No. 3,772,887. This system provides equal acoustical lengths between each of the cylinder exhaust ports and a common exhaust passage but does not attempt to provide equal lengths between the exhaust ports.
An exhaust system for a V-6 engine is disclosed in U.S. Pat. No. 4,187,809. Each bank of three cylinders is provided with an exhaust manifold having channels between the exhaust ports to provide a shortened transmission path for exhaust pulses.